The efficacy of sex offender treatment (SOT) is a matter of ongoing discussion and research in forensic psychotherapy. This study evaluates the efficacy of outpatient SOT after discharge from prison. Recidivism rates of participants treated in outpatient departments for sex offenders in Bavaria between 2008 and 2016 (treatment group, TG; n = 353) were compared with those of a matched group of released offenders without treatment (control group, CG; n = 353). The mean follow-up period was 4.5 years. The primary outcome of interest was whether the rates of reoffending differed significantly between the two groups. We compared general and specific rates of reoffending, time to reoffending, and type of reoffending. The groups differed significantly regarding the rates and time of violent reoffending and reoffending overall, but not regarding sexual reoffending respectively the type of sexual reoffending. The results indicate that outpatient SOT is effective in reducing the general but not the specific risk of reoffending.